There is much evidence for a serotonergic neuron in the enteric nervous system of the gut. It is proposed that this neuron is important for the neuronal modulation of gut motility. The aim of this project is to characterize the development of the serotonergic neuron in the chick gut and to characterize the development of gut motility as measured by the peristaltic reflex in normal chicks and in chicks treated with neurotoxins specific for serotonergic neurons (5, 7 dihydroxytryptamine). Development of serotonergic neurons will be studied with autoradiographic techniques to learn appearance and location, with biochemical techniques to learn appearance of synthesis and release, and with mechanical transducers to learn the appearance of receptors. The development of the peristaltic reflex will be studied with mechanical transducers in isolated gut segments from normal and neurotoxin-treated chicks. Finally, the mechanisms underlying the action of serotonergic neurons will be studied on the cellular level by a combination of methods including vital staining, intracellular recording, intracellular marking with horseradish peroxidase, and light and electron microscopy. Information obtainedmay be useful in understanding the mechanisms underlying pathophysiological conditions of the gut such as paralytic ileus and megacolon.